I've found that people who make the least amount of money tend to work the hardest and/or put up with more crap from people on a day to day basis.
I make half of what my boyfriend makes a month, but I have to run around at work, deal with unrulely, drunk, unreasonable etc. customers on a minute to minute basis.
The difference in pay is because of the schooling required to get to certain jobs: programmers, lawyers, doctors, mechanics, etc. You don't need schooling to become a server, a McDonalds worker, a salesperson, etc.
But yes, they are equally valuable, because without doctors, lawyers (well, we could do w/out them lol), salesmen, and servers, the world wouldn't run like it does.

_________________"I may detest what you say, but I will defend to the death your right to say it." -Voltaire